To obtain a ventilation device to an engine room in a ship which can effectively prevent intrusion of water drops into the engine room through a ventilation cylinder.

In this ventilation device to the engine room in the ship, an air intake chamber with an inlet port of the ventilation cylinder opened is formed high, a spiral rectification plate is provided on the outer circumference on a part located within an air intake chamber of the ventilation cylinder, and an air flow is guided from the air inlet port to the inlet port of the ventilation cylinder so that the flow movement distance of the air is made long and into a turning flow along the outer face of the ventilation cylinder so as to remove water drops.